If you want Darkrai without going to an event, this is what you must do.

1) Activate the Walk Anywhere code on the AR. 2) Go to Canalave City and take the ship to Full Moon Island. 3) When you arrive on the island, start walking East (right). 4) When you have walked far enough New Moon Island will appear. 5) Go to the center of the island, and battle Darkrai.

If you want Shaymin without going to an event, this is what you must do.

1) Activate the Walk Anywhere code on the AR. 2) Go to Pokémon League and walk down the waterfall. 3) Walk east (right) until you reach Route 224. 4) From Route 224, walk north (up) until you come to a long strip of flowers. 5) Go as far up as you can, and battle Shaymin.